1.3. Errors and uncertainties
A subsection of Physics, 9702, through 1. Physical quantities and units
Listing 10 of 89 questions
Define density. shows a cuboidal glass block. z x y (not to scale) A student measures the mass m of the block and the side lengths x, y and z. The measurements are shown in Table 1.1. Table 1.1 quantity measurement m (0.243 ± 0.001) kg x (5.41 ± 0.01) cm y (11.09 ± 0.01) cm z (1.62 ± 0.01) cm Determine the density of the glass. density = kg m–3 Calculate the percentage uncertainty in the density. percentage uncertainty = % The true value of the density of the glass is different from the answer in because of a systematic error in the measurements. Suggest one possible cause of this systematic error.
9702_w24_qp_21
THEORY
2024
Paper 2, Variant 1
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An electromagnetic wave has a wavelength of 85 μm. State the wavelength, in m, of the wave. wavelength = m Calculate the frequency, in THz, of the wave. frequency = THz State the name of the region of the electromagnetic spectrum that contains this wave. The current I in a coil of wire produces a magnetic field. The energy E stored in the magnetic field is given by E = I 2 L where L is a constant. The manufacturer of the coil states that the value of L, in SI base units, is 7.5 × 10–6 ± 5%. The current I in the coil is measured as (0.50 ± 0.02) A. The values of L and I are used to calculate E. Determine the percentage uncertainty in the value of E. percentage uncertainty = %
9702_w20_qp_23
THEORY
2020
Paper 2, Variant 3
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A unit may be stated with a prefix that represents a power-of-ten multiple or submultiple. Complete Table 1.1 to show the name and symbol of each prefix and the corresponding power-of-ten multiple or submultiple. Table 1.1 prefix power-of-ten multiple or submultiple kilo 103 tera (T) ( ) 10–12 In the following list, underline all the units that are SI base units. ampere coulomb metre newton The potential difference V between the two ends of a uniform metal wire is given by V = 4ρLI πd 2 where d is the diameter of the wire, I is the current in the wire, L is the length of the wire, and ρ is the resistivity of the metal. For a particular wire, the percentage uncertainties in the values of some of the above quantities are listed in Table 1.2. Table 1.2 quantity percentage uncertainty d ± 3.0% I ± 2.0% L ± 2.5% V ± 3.5% The quantities listed in Table 1.2 have values that are used to calculate ρ as 4.1 × 10–7 Ω m. For this value of ρ, calculate: the percentage uncertainty percentage uncertainty = % the absolute uncertainty. absolute uncertainty = Ω m
9702_w21_qp_22
THEORY
2021
Paper 2, Variant 2
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Questions Discovered
89